Telephone-circuit



(No Model.)

A. G. BELL. TELEPHONE CIRCUIT.

No. 244,426. Patented July 19,1881.

l Wam/sm @m www UNITED STATES PATENT OFFICE."

ALEXANDER GRAHAM BELL, OF VASHNGTON, DISTRICT OF COLUMBIA.`

TELEPHONE-CIRCUIT.

SPECIFICATION forming part oi' Letters Patent No. 244,426, dated July 19, 1881.

Application lcd .lune 4, 1851..

To all whom fit may concern Be it known that I, ALEXANDER GRAHAM BELL, ot' Washington, in the District ot' Golumbia, have invented a new and useful lmprovement in Telephonie Circuits, which improvement is fully set forth in the following specification.

This invention relates to cables for telephone transmission, and has for its object the production of a cable in which the circuits are so arranged that no disturbance will, in use, arise from their inductive action upon one another. The several circuits are composed each of two wiresa direct and a return wire-forming a metallic circuit.

Inductive disturbance in the telephone and in other electrical instruments connected with a metallic circuit when the latter' is placed in the neighborhood of other electrical circuits arises from the unequal inductive eiiect of the latter upon the two wires, for it is obvious that if the direct and the return wire were affected equally the current generated in one would neutralize and destroy that created in the other. The disturbance can be avoided by placing the two wires in the same inductive relation to the disturbing currents, or, other conditions being the same, by placing them at equal distances from the said circuits. This desired result is accomplished in the present invention. The two wires of each circuit are equidistant, or substantially eqnidistan t, from every other wire in the cable.

The wires which are to form the metallic circuit are covered, one or both, with insulating material, and after being placed together are embedded in or surrounded by insulating` material. The outer layer of insulating` material may in some cases be dispensed with, but in all cases the wires ot' each pair are insulated from each other and from all the other wires,

and are bound together so as to form one strand of the cable. Any desired number of strands are united or held together in any ordinary or suitable way. The two wires ot' each strand may be laid side by side or they may be twisted. The twisted wires are preferred, as giving the most perfect freedom from inductive disturbance, although they are more liable to become injured by handling than the other form on account of the pressure and rubbing action of (No model.)

the wires against each other when the conductor or cable is stretched.

With parallel wires, side by side, it is obvious that in a cable composed of numerous circuits the two wires ot' each strand will not be absolutely equidistant from every 011e oi' the other wires; but the difference in the present invention is made ot' no practical importance by placing wires of each strand very much nearer to each other than to those of any other strand, so much nearer, in fact, that the diierence is only a small fraction of the distance oi either wire of a strand to the nearest wires ot' adjacent strands, and the unneutralized current is inappreciable, or does not create serious disturbance.

The desired relation of circuits is secured by providing a very thin coating of insulating material (such as silk or cotton soaked in parafiine) between the wires of cach strand and surrounding the pair with a much thicker coating, (such as tarred rope, gutta-percha, perite, or india-rubber.) Y/Vith twisted wires the relative distances oi' the wires is of little or no consequence, so far as obviating inductive disturbance is concerned, since by the twist the wires ot'each pair are brought alternately to the same position relative to the other wires. Where both wires oi' each strand are well insulated the external envelope ofthe strand may be omitted, but it is preferred to surround the twisted wires as well as the parallel wires with insulating material.

The accompanying drawings, which form a part of this specification, illustrate what is deemed the best method 0i' carrying the invention into effect.

Figure l represents one of the strands ofthe cable, the View being in elevation, with the insulating-layers partly cut away to show more clearly the construction. Fig. 2 is a view, in crosssection, of the improved cable.

rPhe two wires a b of each strand are small copper wires, equal in size. They each have a coating, c, ot' cotton or silk soaked in parafine, applied in the usual way. After being twisted together they are surrounded with a layer, d, of tarred rope, guttapercha, or other suitable insulating material. A number of these strands are formed into ak cable. As shown, they are bound together by an outer covering, e, which is or may be of rope, Wire, or a combination of materials.

Cables constructed in accordance with this invention may be used above ground, under ground, or under water, and the details of construction can be modified to adapt them to the particular circumstances in which they are to be placed.

Havino' now full f described the said invention and the manner of carrying` the same into effect, I would observe, in conclusion, that I do not claim herein, broadly, as a means for obviating,` the inductive disturbance of electrical circuits upon each other, the arrangement of two wires constituting,` a metallic eircuit in the neighborhood of disturbing-Wires so much nearer to each other than to any ofthe disturbing-wires that they are practically equidistantfrom every one of'said disturbing-Wires; nor do I claim herein the twisting of the insulated wires of the metallic circuit for the purpose indicated, for these matters I have claimed in my application for Letters Patent for improvements in telephonie circuits filed June l0, 1878, of which the present application is a division, and I reserve them for that application 5 but What I do claim herein, and desire to secure by Letters Patent, is-

A cable composed of a number of strands each consisting of two insulated Wires arranged as set forth, the Wires of each strand bein g equidistant, or practically equidistant, from the Wires oi' other strands, substantially as described.

In testimony whereof I have si gned this specification in the presence of two subscribing Witnesses.

ALEXANDER GRAHAM BELL.

Witnesses:

PHILIP MAURO, D. P. COWL. 

